Determination of Anions in Fracking Flowback Water From the Marcellus Shale Using Automated Dilution and Ion Chromatography

Significance of the Topic

Hydraulic fracturing generates large volumes of flowback water enriched in dissolved ions and organic acids. Accurate monitoring of anions such as chloride, bromide, sulfate, acetate and formate is essential to assess environmental impact, ensure compliance with discharge regulations and prevent formation of harmful byproducts. Automated approaches that reduce manual sample preparation and improve analytical reliability are in high demand for routine quality control and environmental monitoring.

Objectives and Study Overview

This study demonstrates an automated workflow combining inline conductivity measurement and ion chromatography (IC) to determine anions and organic acids in Marcellus Shale fracking flowback water. The primary goals were to:

• Trigger sample dilution automatically when conductivity exceeds a preset threshold
• Separate and quantify inorganic anions and organic acids using IC with minimal manual intervention
• Evaluate ion concentration trends across successive flowback fractions

Methodology and Instrumentation

Samples of fracking flowback water (fractions F1–F10) were centrifuged and filtered through 0.2 µm PES membranes. Inline conductivity was measured in the Dionex AS-AP Autosampler equipped with a conductivity and pH accessory. Chromeleon CDS software was configured to trigger a 1:100 dilution when pre-injection conductivity exceeded 1500 µS. Diluted samples (25 µL injection) were analyzed on a Thermo Scientific Dionex ICS-2100 RFIC system using a Dionex EGC III KOH cartridge for eluent generation, Dionex IonPac AG18/AS18 guard and separation columns (4 mm ID), and a Dionex ASRS 300 suppressor in recycle mode.

Main Results and Discussion

Inline conductivity prescreening effectively identified high-salt samples, eliminating repeat injections. Chromatograms showed chloride as the dominant anion (~94 g/L undiluted) and bromide at ~0.89 g/L. Organic acids (acetate, formate) and sulfate were present at low mg/L levels. A chloride calibration curve (1–2000 mg/L) exhibited excellent linearity (r² = 1.00, %RSD = 1.12), confirming quantitative accuracy after 1:100 dilution of samples up to 200 g/L Cl⁻. Ion concentration trends across fractions revealed a tenfold increase in chloride and bromide from F1 to F2, stable elevation thereafter, sharp decline of acetate and propionate/formate after the first fraction, and constant sulfate around 13 mg/L. Spike recovery tests for acetate in high-salt matrices yielded 103–114% recovery, indicating minimal matrix suppression.

Benefits and Practical Applications

This automated dilution and IC approach offers:

• Reduced manual sample preparation and error risk
• Extended column lifetime by preventing overload
• Lower reagent waste and operational costs
• Rapid, reliable quantification supporting compliance monitoring and process optimization

Future Trends and Potential Applications

Emerging directions include extending inline conductivity-triggered dilution to other challenging matrices (e.g., produced waters, high-salinity brines), integrating spectroscopic or mass spectrometric detection, and developing portable IC systems for field deployment, enabling near real-time water quality assessment during hydraulic fracturing operations.

Conclusion

The combination of inline conductivity measurement, automated dilution and ion chromatography provides a robust, efficient solution for analyzing high-ionic strength fracking flowback waters. This workflow enhances analytical throughput, accuracy and sustainability, facilitating routine environmental and process monitoring.

References

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